Fluctuations and latitude effect of cosmic rays at high altitudes and latitudes

Abstract

Using a newly developed ionization chamber, which transmits its information by radio, simultaneous balloon flights were made from widely separated stations in the summer of 1951. Bismarck, North Dakota (geomagnetic latitude, λm, 56°N) was used as a base station. Four flights were made from shipboard going north from Boston and five were made from Thule, Greenland (λm=88°N), simultaneous with those at Bismarck. In all, 28 successful flights were made by the two expeditions. In seeking to determine the geomagnetic effects on the low energy primaries, considerable information was gathered on the radiation that fluctuates from day to day. The following are the chief experimental findings together with some of the conclusions that may be drawn. (1) The fluctuations in the primary radiation at 90 000 feet were as much as 10 percent in a few days. (2) These were simultaneous (except as noted in the text) and very close to the same amount at the two stations. (3) The magnitude of the fluctuations at high altitudes was considerably larger than the geomagnetic effect between Bismarck and Thule. (4) The radiation that fluctuated contained both high (> 15 Bev/c) momentum and low (down to 1.5 Bev/c) momentum particles. (5) There was a good correlation between the fluctuations in the radiation at high altitudes and the fluctuations in the neutron and meson components at ground level. (6) The fact that no particles fluctuated at Thule that did not also fluctuate at Bismarck leads us to conclude that there are few, if any, low energy particles coming in at Thule that are not also present at Bismarck, otherwise they too would be expected to vary. (7) From the manner in which the fluctuating radiation is absorbed in the atmosphere, it is concluded that the fluctuations cannot be due to heavy primaries alone. Rather it appears that the particles that fluctuate are of the same nature as the other incoming particles but have somewhat less energy per particle. (8) Varying magnetic fields of the geomagnetic axially symmetrical type are discarded as being able to produce the kind of fluctuations observed. A more satisfactory mechanism appears to be varying electric fields. (9) There was a negative latitude effect in the total ionization at intermediate altitudes (30 000 to 50 000 feet) at high latitudes. This we attribute to the greater importance of μ-meson decay in the warmer air of the stratosphere which exists at the more northerly latitudes. The temperature coefficient arrived at is -0.19 percent °C-1. (10) There was a positive latitude effect in the total ionization above 60 000 feet at high latitudes. Evidence is presented to show that this is not likely to be due either to atmospheric effects or to low energy particles admitted by the earth's magnetic field above 66°N. We attribute this increase to the shadow effect of the earth. (11) The absence of particles with momenta in the range 1.5 to 0.6 Bev/Zc (0.8 to 0.14 Bev for protons), shown by (a) a lack of increase of ionization at very high altitudes between geomagnetic latitudes 58° and 66°N, (b) the absence of an increase of area under the ionization-depth curve at latitudes north of λm=58°N, and (c) the absence of any particles that fluctuate at Thule that do not also fluctuate at Bismarck, indicates a cutoff of the primary particles. (12) This cutoff we attribute to a general solar magnetic field. The magnetic moment required is 0.65×10^34 gauss-cm3 corresponding to a field at the solar equator of 19 gauss. (13) Any diurnal effect on cosmic rays due to such a magnetic moment would normally be hidden by the daily fluctuations of the primary particles.

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